Design of store-release covers to minimize deep drainage in the mining and waste-disposal industries: results from a modelling analyses based on ecophysiological principles

Sustainable long-term storage of municipal waste and waste rock from mining activities in waste dumps (either above or below the land surface) requires minimization of percolation of rainwater into and then through stored waste material. There has been increasing attention given to the use of store-release covers (transpirational covers) to achieve this. However, the design of such covers remains problematic because of the unique combinations of weather, vegetation composition, soils and their interactions that determine the efficacy of each design that could be available for the construction of the covers. The aim of the work described here was to use ecophysiological knowledge of soil-plant-atmosphere (SPA) interactions through the application of a detailed mechanistic model of the SPA continuum. We examined the relative influence of soil depth, soil texture, leaf area index and rainfall as determinants of rates of evapotranspiration and water budget for several different theoretical cover designs. We show that minimizing deep drainage requires a cover that has the following attributes: (i) a water storage capacity that is large enough to store the volume of water that is received as rainfall in above-average wet months/seasons; (ii) a root distribution that explores the entire depth of the cover; (iii) a leaf area index that is present all year sufficient to evapotranspire monthly rainfall; and (iv) takes into account the intra-annual and inter-annual variability in rainfall and other climatic variables that drive ET.